As the investigation continues into the deadly blasts at the Boston Marathon on Monday, authorities hope evidence found at the scene will shed light as to who or why someone would commit what President Obama called a "heinous and cowardly act."

Authorities said Tuesday that the explosive devices were likely built in a pressure cooker and hidden in a black backpack or bag filled with fragments of nails and BBs. Authorities said they found pieces of black nylon at the scene and those pieces were taken to a FBI laboratory for more analysis.

Krystle Campbell, 29; Martin Richard, 8; and an unidentified graduate student from Boston University died in the bombings. Dozens of people were injured, many losing limbs, in the blasts and remain hospitalized.

The first blast occurred near the finish line on Boylston Street in Boston. About 12 seconds later, a second explosion occurred about 50 to 100 yards from the first one. The explosions left Boston's Copley Square in smoke as first responders hurried to the scene. The blasts were powerful enough to blow out windows of nearby buildings.

After the blast, witnesses reported seeing many people bleeding profusely and some without arms or legs. The blasts occurred around 2:45 p.m. ET Monday, nearly an hour after the first finishers completed the marathon.

No one has claimed responsibility for the bombings and the motive is not yet known. Authorities said they are questioning people in connection with the bombings, but there are no suspects in custody.

"This is a horrific day in Boston," Massachusetts Gov. Deval Patrick said in a statement Monday. President Obama vowed to the nation that "we will find out who did this."

HLNtv.com continued to follow the story as events unfolded in our live blog, which you can read below. Please check out our sister site, CNN.com, for the latest details into the bombing investigation.

7:55 p.m. ET: The Chinese Consulate in New York confirms that a Chinese national was among the three killed died in the bombings. CNN is reporting that the person was a grad student at Boston University. However, the person's name has not yet been released.

6:56 p.m. ET: At least 13 of the 183 people injured in Monday's bombings have had amputations, according to CNN.

6:19 p.m. ET: WHDH has provided images to the FBI that show a bag near the bomb site.

5:51 p.m. ET: A third victim killed in Monday's bombings has been identified as a graduate student from Boston University, but that person's name has not yet been released.

5:23 p.m. ET: Patty Campbell, mother of Krystle Campbell who died in the bombings, tearfully told reporters that her daughter was a “fun-loving girl” and she “had a heart of gold.”

5:16 p.m. ET: Patrick says President Obama will attend an interfaith service in Boston for the bombing victims at 11 a.m. Thursday.

5:15 p.m. ET: Massachusetts Gov. Deval Patrick says there is a sustained need for blood donations. He asked people to please donate in the coming weeks.

5:08 p.m. ET: Rick DesLauriers, FBI Special Agent in Charge, says authorities have recovered pieces of black nylon and fragments of nails and BBs from the scene of both blasts. He says authorities believe the explosive devices were likely in a black nylon bag or backpack. He also said the bag was likely heavy due to the contents inside.

5 p.m. ET: The Boston Athletic Association released a statement that reads in part:

We are cooperating with the City of Boston, the Commonwealth of Massachusetts, and all federal law enforcement officials in the investigation and the effort to bring those responsible for this tragedy to justice, so we are limited in what information we can provide.

Boston is strong. Boston is resilient. Boston is our home. And Boston has made us enormously proud in the past 24 hours. The Boston Marathon is a deeply held tradition – an integral part of the fabric and history of our community. We are committed to continuing that tradition with the running of the 118th Boston Marathon in 2014.

4:37 p.m. ET: Dechert says some patients have been upgraded from the critical list, but many will still face more surgeries in the coming days.

4:35 p.m. ET: Dr. Tracey Dechert, a trauma surgeon at Boston Medical Center, says the facility took in 23 patients after the bombing. She says patients at the hospital are "progressing."

3:59 p.m. ET: According to CNN, the number of injured in Monday's terror attack at the Boston Marathon is now at 183. Of the 183 injured, at least 23 received critical injuries, at least 40 received serious injuries, and at least 9 are children.

2:45 p.m. ET: Leaders from public safety unions in Boston have announced a $50,000 reward for the information leading to the arrest and conviction of those responsible for the terrorist attack yesterday, as well as the establishment of a Fund that will aid the victims of the attack. Anyone with information is asked to call the Boston Police Homicide Unit at 617-343-4470.

2:25 p.m. ET: According to a senior U.S. official, "there is no reporting indicating a foreign connection or any reaction from al Qaeda" to the Boston Marathon bombings. The official also said there were "no known terrorist threats to Boston or (the) marathon."

2:15 p.m. ET: Krystle Campbell, a 2001 graduate of Medford High School in Massachusetts, died in Monday's Boston Marathon attack, the town's mayor said Tuesday. She was one of three people killed in the terror attack.

1:16 p.m. ET: Boston-area hospitals have discharged at least 51 of the 174 people injured in Monday's marathon bombings, according to a CNN tally.

12:59 p.m. ET: Bill Richard, father of 8-year-old bombing victim Martin Richard, has released the following statement:

"My dear son Martin has died from injuries sustained in the attack on Boston. My wife and daughter are both recovering from serious injuries. We thank our family and friends, those we know and those we have never met, for their thoughts and prayers. I ask that you continue to pray for my family as we remember Martin. We also ask for your patience and for privacy as we work to simultaneously grieve and recover. Thank you.”

12:44 p.m. ET: A law enforcement official told CNN Tuesday that it's "likely but not certain" that a timer was attached to an explosive device involved in the Boston Marathon bombings, as opposed to being activated by a cell phone.

12:42 p.m. ET: At least two Saudi nationals were injured in the Boston Marathon bombings, a Saudi embassy official told CNN. One is a male student, 20, the other is a woman who was at the marathon with her husband and child, the source said. Neither injured Saudi is considered a suspect in the attacks, the official said, citing U.S. officials.

12:41 p.m. E.T.: Sports Illustrated has released this week's cover: Boston. The issue features documentary-style coverage of the Boston Marathon terror attack.

12:25 p.m. ET: One bomb used in the Boston Marathon terror attack appears to have been placed inside a metal pressure cooker hidden inside a backpack, a federal law enforcement official with knowledge of the investigation told CNN on Tuesday.

11:45 a.m. E.T.: Rachel Moo, the teacher of 8-year-old Boston victim Martin Richard, posted this photo on Facebook, with the message: "NHCS second graders are organizing a Peace Walk to promote peace in our neighborhoods and in the city of Boston.” The peace walk took place in May, 2012.

11:35 a.m. ET: President Obama, in a briefing, calls the Boston bombings a "heinous and cowardly act" that the FBI is investigating as an act of terrorism. "Any time bombs are used to target civilians, it is an act of terrorism," Obama said, adding that it remained unclear who carried out the attack and why.

11:14 a.m. ET: According to Boston Children's Hospital, seven of the 10 patients admitted there after the Boston Marathon explosion have been discharged, but a 10-year-old boy and a 9-year-old girl remain in critical condition. A 2-year-old boy has been listed in good condition.

11:11 a.m. ET: President Barack Obama will make a statement to reporters at 11:30 a.m. ET on Tuesday, the White House has announced.

10:45 a.m. ET: President Obama has ordered the U.S. flag to be flow at half-staff "at the White House and upon all public buildings and grounds, at all military posts and naval stations, and on all naval vessels of the Federal Government in the District of Columbia and throughout the United States and its Territories and possessions until sunset, April 20, 2013."

10:35 a.m. ET: Doctors operating on people wounded in the Boston Marathon attack found many sharp nail-like objects in victims' bodies and had to perform at least four amputations, said Dr. George Velmahos, head of trauma care at Massachusetts General Hospital.

10:11 a.m.ET: More than 170 injuries have been recorded at hospitals in Boston and other areas, Police Chief Ed Davis said in a briefing about the Boston Marathon terror attack investigation. At least 17 of those people are in critical condition.

10:05 a.m. ET: Law enforcement intends to sift "through every frame of every video" at the scene of the Boston Marathon terror attack, Boston Police Chief Ed Davis says.

9:54 a.m. ET: Boston's police chief says the crime scene has been reduced from 15 to 12 blocks, and it will be narrowed as the investigation proceeds.

9:41 a.m. ET: No unexploded devices were found in Boston, according to Massachusetts governor, who is currently holding a news conference.

9:09 a.m. ET: The New York Stock Exchange has announced it will observe a moment of silence for the victims of the Boston terror attacks from 9:20 to 9:21 a.m. Tuesday morning.

8:19 a.m. ET: According to a senior White House official, F.B.I. director Robert Mueller will be at the White House this morning to brief President Obama on the latest developments in the bombing, along with Homeland Security Advisor Lisa Monaco and others.

6:34 a.m. ET: We now have a photo of Martin Richard, the 8-year-old boy who the Boston Globe reports was killed in the terror attack. He is the son of Denise and William Richard.

6:14 a.m. ET: A White House Official tells HLN: Overnight, the President received updates from his Assistant for Homeland Security and Counterterrorism Lisa Monaco on the ongoing response efforts and investigation into the explosions in Boston, including the continuing federal support for those activities.

Later this morning the President will receive a briefing from his Assistant for Homeland Security and Counterterrorism Lisa Monaco, FBI Director Robert Mueller and other senior members of his team.

Tuesday, April 16, 3:30 a.m. ET:The Boston Globe reports the identity of the 8-year-old boy killed in Monday's bombings is Martin Richard. The paper reports the boy's mother and sister also "suffered grievous injuries." At this hour 2 others are confirmed dead, and at least 144 injured in the blasts.

10:15 p.m. ET: At a press conference, trauma surgeon Dr. Peter Fagenholz said there are 29 wounded people being treated at Massachusetts General Hospital, including eight in critical condition. He said many of the patients had injuries to their lower extremities, and that doctors had performed several amputations.

8:52 p.m. ET: Police Commissioner Ed Davis now says three people have died in the bombings. Authorities are still looking for additional devices, but they say their main focus is the Copley Square area.

8:47 p.m. ET: Patrick says that there will be increased security on Tuesday across the city, and he urged residents to report any suspicious individual or activity.

8:46 p.m. ET: Patrick: Boston will be open tomorrow, but it won't be "business as unusual."

8:45 p.m. ET: Massachusetts Gov. Deval Patrick says the National Guard has secured the crime scene near the finish line of the Boston Marathon.

8:19 p.m. ET: The NBA announced that Tuesday's game between the Indiana Pacers and the Boston Celtics at TD Garden has been canceled and the game will not be rescheduled.

8:13 p.m. ET: CNN has obtained a bulletin from law enforcement officials to be on the lookout for a darker-skinned or black male wearing a black sweatshirt and a black backpack who tried to gain access to a restricted area of the marathon five minutes before the first explosion.

7:52 p.m. ET: Authorities are searching for a Penske truck that was denied access to the marathon before the blasts.

7:50 p.m. ET: Hospitals now report that 132 people were injured from explosions at the Boston Marathon. Hospitals also report there have been at least 10 amputations. A terrorism expert told CNN's Deb Feyerick that doctors are pulling ball bearings out of people's legs.

7:37 p.m. ET: CNN has confirmed that a 8-year-old boy was one of the two killed in Monday's twin blasts at the Boston Marathon.

7:07 p.m. ET: Cardinal Timothy Dolan released the following statement after the bombings:

The tragic end to the Boston Marathon April 15 reminds us all that evil exists and that life is fragile.

The deaths and injuries of people gathered for the celebration on Patriots Day in Boston calls on all of us to pray for the souls of those killed the healing of those injured and the restoration of peace for all of us unsettled by the bombings at a world renowned sporting event.

Our special prayers are with the Archdiocese of Boston and the people there who are working in the aftermath of this crisis to address those wounded in so many ways by these events.

The growing culture of violence in our world and even in our country calls for both wise security measures by government officials and an examination by all of us to see what we can personally do to enhance peace and respect for one another in our world.

6:50 p.m. ET: At least 110 people have been treated at hospitals after Monday's bombings, according to spokespeople from those facilities.

6:33 p.m. ET: Rep. Bill Keating (D-Massachusetts) told CNN that authorities found two unexploded devices -- one at the Mandarin Oriental hotel and another at an undisclosed location. Those devices are being examined by authorities.

6:32 p.m. ET: HLN affiliate WHDH is reporting a 8-year-old was one of the two people killed in the Boston bombings.

6:21 p.m. ET: A spokeswoman for Boston's Children's Hospital says there were treating six children injured in the twin blasts. The spokeswoman says their injuries are not considered life-threatening.

6:14 p.m. ET: Obama: "We will find out who did this." The president did not to use the words terrorism as he addressed reporters and the nation.

6:13 p.m. ET: Obama: "We still don't know who did this or why and People shouldn't jump to conclusions before we have all the facts. The president said those responsible will "feel the full weight of justice."

6:10 p.m. ET: President Obama: "The American people will say a prayer for Boston tonight."

6:04 p.m. ET: Former Homeland Security Adviser Fran Townsend told CNN that sources have told her that the FBI has deemed today's twin bombings as a terrorist attack.

5:59 p.m. ET: Boston Police Commissioner Ed Davis clarified his earlier statement that the incident at the JFK Library was "fire-related." He said they are investigating the twin blasts at the Boston Marathon.

Davis said the area around the bombings will be closed for at least 24 hours if not more as authorities investigate the scene. He said authorities received "no specific intelligence" that anything was going to happen.

5:55 p.m. ET: Boston Mayor Thomas Menino: "This is a tragedy."

5:45 p.m. ET: President Obama is expected to make a statement around 6:10 p.m. ET about the Boston bombings. Boston Mayor Thomas Menino is also expected to speak later tonight.

5:41 p.m. ET: When asked directly about reports coming from the New York Post claiming a Saudi National is being held in custody in relation to the Boston bombings, Neva Coakley, a spokeswoman for Boston Police, says "I don't know where they got that from. We don't have anyone in custody."

5:37 p.m. ET: Police are now saying that the incident at the JFK Library was "fire-related."

4:54 p.m. ET: "If anybody saw anything at this incident .. they should call us at 1-800-494-TIPS," Davis said. Families looking for loved ones are urged to call 617-635-4500.

"People should be calm but they should understand that we need all the information that we can get available to us," Davis said.

4:53 p.m. ET: Boston police is recommending that people stay in their homes and hotel rooms.

4:52 p.m. ET: Davis said an explosion also occurred at the John F. Kennedy Presidential Library & Museum about 30 minutes ago. Davis said it's not known if that incident is related to the prior blasts.

4:44 p.m. ET: Massachusetts Gov. Deval Patrick issued the following statement: “This is a horrific day in Boston. My thoughts and prayers are with those who have been injured. I have been in touch with the President, Mayor Menino and our public safety leaders. Our focus is on making sure that the area around Copley Square is safe and secured. I am asking everyone to stay away from Copley Square and let the first responders do their jobs.”

4:41 p.m. ET: A government source tells CNN that a third explosive device has been disabled.

4:39 p.m. ET:

Mass General has 19 patients, six critical, including multiple amputations #WCVB#Boston

4:37 p.m. ET: Gary Meagher, NHL Senior Vice President, Public Relations and Media, tells CNN that as of now, this evening’s Boston Bruins game against the Ottawa Senators is still on as scheduled for 7 p.m. ET in Boston.

4:35 p.m. ET: President Obama was notified about the bombings around 3 p.m. ET and contacted Boston Mayor Tom Menino and Massachusetts Gov. Deval Patrick to "express his concern for those who were injured" and "his administration is ready to provide needed support as they respond to the incident."

4:32 p.m.ET: According to a senior U.S. official citing a bulletin sent to federal officials, local law enforcement, a bomb squad and SWAT teams are on the scene investigating other devices. All federal buildings in the Boston area have been shut down.

4:25 p.m. ET: A law enforcement source told CNN's Joe Johns that another explosive device has been found. There is no word on the location.

4:22 p.m. ET: A press conference will be held at 4:30 p.m. at the Westin Hotel to discuss the incident.

4:20 p.m. ET: Rep. Ed. Markey (D-Mass.) released a statement: "I am disturbed and saddened by the explosions at the site of the Boston Marathon this afternoon. We all are grateful for the first responders who rushed to the scene to help the victims. The heart of the city is hanging heavy, and our thoughts and prayers are with everyone affected by this senseless tragedy."

4:15 p.m. ET: The number of people injured in the blasts is now at 28.

4:07 p.m. ET: There is heightened security in New York and Washington, D.C. after the blasts in Boston.

4:03 p.m. ET: Two people are dead and at least 23 were hurt in the explosions, according to Boston Police.

3:59 p.m. ET: Official tweet from Boston Marathon.

There were two bombs that exploded near the finish line in today's Boston Marathon. We are working with law... fb.me/1HdL4nLXX

3:47 p.m. ET: CNN's John King says a state government source told him that some people are being treated at a medical tent set up for runners.

3:45 p.m. ET: Four patients were taken to Massachusetts General Hospital, a spokeswoman said. Onlooker Josh Matthews said he heard the blast. "We just heard a lot of sirens, and people were kinda frantic. It was a bad situation, so we got out of there."

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